This invention relates to an optical module. In particular, the invention relates to an Arrayed Waveguide Grating (AWG) module.
Arrayed Waveguide Grating (AWG) devices are commonly used in Wavelength Division Multiplexing (WDM) systems for multiplexing (combining) optical signals of different wavelengths onto a single optical signal. An AWG device operating in this way shall be considered as operating in a forward sense. AWG devices can also be operated in a reverse sense for demultiplexing (splitting) a multiplexed optical signal into a plurality of constituent optical signals of different wavelengths. The different wavelengths correspond to different channels in the WDM system with channel spacings typically being in the order of 1 nm.
An AWG device has two optical interfaces arranged at opposite ends of the device. Each optical interface can function as an input or an output of the AWG device depending on whether the AWG device is operating in a forward or reverse sense. In the forward sense, the first optical interface functions as an input for receiving multiple optical signals via separate optical fibers. The optical fibers are bundled at the input interface of the AWG device, and are accurately aligned in a side-by-side arrangement with the individual optical channels of the input. The second optical interface functions as an output for outputting a single multiplexed optical signal onto a single output optical fiber. The single output optical fiber is accurately aligned at the output interface of the AWG device. When the AWG device operates in the reverse sense, the output interface functions as an input, and the multiple channel input interface functions as a multiple channel output interface.
The optical fibers are attached to the optical interfaces of the AWG device by means of a V-groove block. The attachment of the optical fibers to the AWG device is a one time process which must be performed with precise instruments under well-defined temperature conditions. For this and other reasons, AWG devices are typically supplied with the optical fibers pre-attached, and with the AWG device contained in a protective housing. AWG devices assembled in this way are available from manufacturers such as NTT Electronics (NEL) of Japan, and shall be referred to herein as AWG modules.
FIG. 1 shows a known AWG module 100 installed on a board 110 of a rack-mount system. The board 110 can be mounted horizontally or vertically in the rack-mount system. When mounted, a front edge 112 of the board is generally exposed to provide input and output connections to the board 110.
The AWG module 100 generally comprises a AWG device 102, a housing 120, and a series of optical fibers 103, 104. Optical fiber 103 is connected at one end to an optical interface of the AWG device 102, and at the other end to an optical connector 105. An optical fiber bundle 104, comprising 32 individual optical fibers, is connected at one end to the AWG device 102, and at the other end to four separate 8-channel optical connectors 106, 107, 108, 109. The optical fiber bundle 104 is grouped into 4 sets of 8 optical fibers, each set being represented by a single line in FIG. 1. Each set of 8 optical fibers is covered by a protective sleeve or sheath, and is coupled to a different optical connector 106, 107, 108, 109. The protective sleeves help to prevent the delicate fibers from breaking.
The optical connectors 105, 106, 107, 108, 109 act as inputs or outputs for the AWG module 100 and the board 110.
Each optical fiber in the optical fiber bundle 104 corresponds to a communication channel. Accordingly, the AWG module of FIG. 1 is a 32 channel AWG module. AWG modules are also available, for example, in 8, 16, and 40 channel versions.
The AWG module 100 includes a housing 120 which surrounds and helps to protect both the AWG device 102 and the attachments between the AWG device 102 and the optical fibers 103, 104. The optical fibers 103, 104 extend outside of the housing 120 via openings at opposite ends of the housing 120. Strain relief bushings 122, 124 are provided on the housing 120 to prevent the optical fibers 103, 104 from kinking against the leading edge of the openings.
In general, optical fibers used in AWG modules are extremely delicate and can be damaged when the radius of curvature along their length is reduced below a minimum value, typically about 17 mm. The radius of curvature of an optical fiber is significantly reduced when the fiber is bent too tightly or when the fiber is kinked against a sharp edge. Damage to an optical fiber can also occur from direct impact or abrasion to an unprotected region of the fiber. In the AWG module 100 of FIG. 1, the vulnerable regions of the fibers are the exposed regions, especially around the optical connectors 105, 106, 107, 108, 109, and the bushings 122, 124.
As mentioned, the attachment of the optical fibers to the AWG device is a precision operation, and the AWG module of FIG. 1 includes a housing to help protect the attachments between the AWG device 102 and the optical fibers 103, 104. Nevertheless, the attachments between the AWG device 102 and the optical fibers 103, 104 are prone to damage when tensile forces are applied to the optical fibers 103, 104 pulling the fibers out from the housing 102. The strain relief bushings 122, 124 provide no protection from tensile forces applied to the fibers.
AWG modules are typically shipped to customers in protective packaging. The customer then removes the AWG module from the packaging, and installs the AWG module onto a board for use in a rack-mount system, as shown in FIG. 1. The steps of packaging the AWG module, shipping the AWG module, removing the AWG module from the packaging, and installing the AWG module onto a board all increase the likelihood of the AWG module being damaged. Damage can occur to the optical fibers themselves, or to the attachments between the AWG device 102 and the optical fibers 103, 104. To help prevent damage to the AWG module, the steps mentioned above are performed with great care, usually requiring more than one person.
Improvements in packaging techniques for the AWG module can reduce the likelihood of damage during shipping but often result in greater labor in the packing and unpacking steps. For example, mechanical clips can be used to hold down the optical fibers and connectors in a shipping box but require delicate handling to clip and unclip the fibers.
If a customer is not made aware of the careful handling requirements for the AWG module then damage can often occur to the AWG module which can be costly and time consuming.